Active retrotransposition by a synthetic L1 element in mice

Area of Science:

• Genetics
• Molecular Biology
• Genomics

Background:

• Long interspersed element type 1 (L1) retrotransposons are mobile genetic elements found in mammals.
• Native L1 elements exhibit limited activity in mice when used as transgenes.
• A synthetic L1 element, ORFeus, was previously developed with enhanced activity in cell culture.

Purpose of the Study:

• To investigate the in vivo retrotransposition activity of the synthetic L1 element, ORFeus, in a transgenic mouse model.
• To assess the potential of ORFeus as a tool for in vivo mutagenesis.

Main Methods:

• Development of a transgenic mouse model expressing ORFeus under a constitutive heterologous promoter.
• Analysis of germ line and somatic retrotransposition events in ORFeus-expressing mice.
• Precise mapping of insertion sites in the mouse genome.

Main Results:

• ORFeus demonstrated significant germ line retrotransposition, with frequencies over 20-fold higher than native L1 elements.
• Somatic transposition events were observed in 100% of analyzed animals, with an average of 17 easily recoverable insertions per animal.
• Nearly 200 insertions were mapped, showing a random distribution relative to genomic features like transcription units and GC content.

Conclusions:

• The synthetic L1 element ORFeus exhibits robust in vivo retrotransposition activity in both germ line and somatic tissues.
• ORFeus shows promise as an effective tool for in vivo mutagenesis in mice.
• The random distribution of insertions supports its utility for genome-wide mutagenesis screens.